Microstructure Modification in Copper Interconnect Structures

ABSTRACT

A metal interconnect structure and a method of manufacturing the metal interconnect structure. Manganese (Mn) is incorporated into a copper (Cu) interconnect structure in order to modify the microstructure to achieve bamboo-style grain boundaries in sub-90 nm technologies. Preferably, bamboo grains are separated at distances less than the “Blech” length so that copper (Cu) diffusion through grain boundaries is avoided. The added Mn also triggers the growth of Cu grains down to the bottom surface of the metal line so that a true bamboo microstructure reaching to the bottom surface is formed and the Cu diffusion mechanism along grain boundaries oriented along the length of the metal line is eliminated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor structures. Moreparticularly, the present invention relates to metal interconnectstructures having large grain sizes at a bottom of a metal interconnectline and methods of manufacturing the same.

2. Description of the Related Art

Current sub-90 nm copper interconnect technology has a non-bamboomicrostructure, that is, a microstructure without bamboo-like featuresin lines and vias. The non-bamboo microstructure leads to concernsassociated with copper diffusion such as electromigration and stressvoiding.

There are currently three different modes of copper diffusion. One modeis copper diffusion along grain boundaries of a copper interconnectstructure. Another mode is copper diffusion at a surface of a copperinterconnect structure, that is, at an interface at which the copperinterconnect structure adjoins another material. An alternate mode iscopper bulk diffusion through grains, that is, across an interface atwhich two grain boundaries meet. Typically, the rate of diffusion ishigher for copper diffusion along grain boundaries and lower for copperbulk diffusion through grains. Thus, it is optimal to form a copperinterconnect structure containing a metal line in which the metal linehas a bamboo-like pattern in the grain microstructure, or a “bamboomicrostructure.” In a bamboo microstructure, the lateral width of agrain is the same as the width of the metal line or the metal via. Thelength of the grain is greater than the width of the metal line so thatgrain boundaries look like a stalk of a bamboo plant with notchedsegmentation.

It is optimal to have a bamboo microstructure where grains span thewidth and height of a line or via. The phenomenon of electromigrationoccurs when a current flowing in the line, due to an externally appliedfield, leads to a net drift of copper (Cu) ions in the direction of theelectron flow. The drift eventually will lead to line failure due toloss of copper at divergent sites such as grain boundaries and materialinterfaces. Because electrical current flows along the direction of ametal line and any electromigration is forced to occur “through,” thatis, substantially perpendicular to the plane of grain boundaries, thebamboo microstructure offers significantly more resistance toelectromigration than non-bamboo microstructures. The bamboomicrostructure essentially shuts down diffusion along grain boundaries,because bamboo grain boundaries are substantially at right angles to thecurrent flow.

An alternative way of suppressing electromigration in a metalinterconnect structure exists. If the length of a metal line is lessthan the “Blech” length, copper ion motion will not occur, shutting downthe electromigration process. Mechanical stress at lengths less than the“Blech” length opposes the drift of copper ions. A typical Blech lengthis 10 microns for current interconnect structures consisting of copper.In principle, designing all interconnect metal lines shorter than the“Blech” length would solve the problem. In practice, such a limitationputs a severe constraint on the design and layout of an interconnectstructure, and practically renders such layouts impractical.

In a related patent, U.S. Pat. No. 7,843,063, commonly assigned, it isdisclosed that cobalt (Co) has a similar property, promoting normalgrain growth (growth of all orientations simultaneously) or abnormalgrain growth (growth of certain orientations preferential to others) inthe fine lines and vias leading to bamboo grains (spanning the linewidth and height). Although, cobalt (Co) and manganese (Mn) have similarproperties, Mn has a better optimal percentage over the use of Co.

The use of Cu-Mn seed layers has been contemplated in order to form“self-forming” diffusion barriers. The Mn is placed in the Cu seed layerand after thermal treatment diffuses to interfaces reacting with oxygen(O) to form manganese oxide (MnO) and possibly manganese silicate(MnSiO) layers. These layers at the dielectric-copper (Cu) interface orbarrier-copper (Cu) interface act as diffusion barriers. Somepublications that describe the use of MnO as a diffusion barrier are:

J. Koike et al., Appl. Phys. Lett. 87, (2005), 041911; J. Iijima et al.,Proc. of IITC, (2006), 246; T. Watanabe et al., Proc. of IITC, (2007),7; M. Haneda et al., Proc. of AMC (2207), 59.

Suppressing copper diffusion without resorting to use of a design rulestipulating that all metal interconnect lines be shorter than the“Blech” length is needed. Thus, there exists a need for metalinterconnect structures having fine feature sizes such as sub-90 nmmetal lines, i.e. metal lines having a width less than 90 nm, andcontaining bamboo microstructures so that copper diffusion andassociated complications can be avoided. A bamboo grain, one spanningthe width and height of an interconnect or via, every “Blech” length (10μm), will substantially stop electromigration along grain boundaries.

SUMMARY OF THE INVENTION

The present invention incorporates manganese into a copper interconnectstructure in order to modify the microstructure to achieve bamboo-stylegrain boundaries in sub-90 nm technologies.

According to an embodiment of the present invention, a metalinterconnect structure is provided. The metal interconnect structureincludes: a dielectric material layer containing a recessed linepattern; a metallic barrier layer abutting the dielectric material layerat sidewalls of the recessed line pattern and overlying an entirety ofthe dielectric material layer; a copper-containing seed layer abuttingthe metallic barrier layer and overlying an entirety of the dielectricmaterial layer; and a copper-containing layer including electroplatedcopper and abutting the copper-containing seed layer, wherein at leastone of the copper-containing seed layer and the copper-containing layerincludes a copper-manganese alloy, and wherein the copper-containingseed layer and the copper-containing layer form a bamboo grain withinthe recessed line pattern, the grain size measured at a bottom surfaceof the copper-containing layer exceeding a width of the copper-manganesealloy line at least every “Blech” length.

According to a further embodiment of the present invention, anothermetal interconnect structure is provided. The metal interconnectstructure includes: a dielectric material layer containing a recessedline pattern; a metallic barrier layer abutting the dielectric materiallayer at sidewalls of the recessed line pattern and overlying anentirety of the dielectric material layer; a copper-containing seedlayer abutting the metallic barrier layer and overlying an entirety ofthe dielectric material layer; a copper-containing layer includingelectroplated copper and abutting the copper-containing seed layer,wherein the copper-containing seed layer and the copper-containing layerform a bamboo grain within the recessed line pattern, the grain sizemeasured at a bottom surface of the copper-containing layer exceeding awidth of the copper-manganese alloy line at least every “Blech” length;and a copper-manganese alloy cap layer abutting the copper-containinglayer.

According to another embodiment of the present invention, a furthermetal interconnect structure is provided. The metal interconnectstructure includes: a plated copper layer containing a line pattern; acopper-manganese seed layer having an atomic concentration of manganesefrom about 1 ppm to about 20 atomic percent at the bottom surface of theplated copper line sandwiched between the plated copper line and abarrier layer all of which are patterned, wherein a grain size measuredat a bottom of the copper-manganese alloy line exceeds a width of thecopper-manganese alloy line at least every “Blech” length; and a barrierand dielectric layer surrounding the copper manganese alloy line.

According to a further embodiment of the present invention, a method offorming a metal interconnect structure is provided. The method includes:providing a dielectric material layer containing a recessed linepattern; forming a metallic barrier layer on the dielectric materiallayer at sidewalls of the recessed line pattern; forming acopper-containing seed layer on the metallic barrier layer; andelectroplating a copper-containing layer on the copper-containing seedlayer, wherein at least one of the copper-containing seed layer and thecopper-containing layer includes a copper-manganese alloy containing amanganese concentration from about 1 ppm to about 10 atomic percent.

According to another embodiment of the present invention, a furthermethod of forming a metal interconnect structure is provided. The methodincludes: providing a dielectric material layer containing a recessedline pattern; forming a metallic barrier layer directly on thedielectric material layer at sidewalls of the recessed line pattern;forming a copper-containing seed layer directly on the metallic barrierlayer; electroplating a copper-containing layer directly on thecopper-containing seed layer; and forming a copper-manganese alloy caplayer containing a manganese concentration from about 1 ppm to about 50atomic percent directly on the copper-containing layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and elements of the present invention are set forth withrespect to the appended claims and illustrated in the drawings.

FIG. 1 illustrates a schematic cross section of a first embodiment ofthe metal interconnect structure of the present invention.

FIG. 2 illustrates a schematic cross section of a second embodiment ofthe metal interconnect structure of the present invention.

FIG. 3 illustrates a schematic cross section of a third embodiment ofthe metal interconnect structure of the present invention.

FIG. 4A-4E illustrates the method of manufacturing the metalinterconnect structure of the present invention.

FIG. 5 illustrates a schematic cross section of a fourth embodiment ofthe metal interconnect structure of the present invention.

FIG. 6 illustrates a plot of percentage decrease in sheet resistanceversus time at room temperature for a 500 nm plated copper film on a 30nm Cu—Mn seed layer on silicon oxide.

FIG. 7 illustrates a plot of percentage decrease in sheet resistanceversus time at room temperature for a 300 nm plated copper film on a 30nm Cu—Mn seed layer on silicon oxide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes embodiments of the present invention withreference to the drawings. The embodiments are illustrations of theinvention, which can be embodied in various forms. The present inventionis not limited to the embodiments described below, rather representativefor teaching one skilled in the art how to make and use it. Some aspectsof the drawings repeat from one drawing to the next. The aspects retaintheir same numbering from their first appearance throughout each of thepreceding drawings.

The present invention incorporates manganese (Mn) into a copper (Cu)interconnect structure in order to modify the microstructure to achievebamboo-style grain boundaries in sub-90 nm technologies. Preferably,bamboo grains are separated at distances less than the “Blech” length sothat copper (Cu) diffusion through grain boundaries is avoided. Themanganese (Mn) can be incorporated into a copper (Cu) seed layer to beformed under a metal line, as a capping layer to be formed over a metalline, or during a plating process Annealing the copper (Cu) interconnectstructure at room temperature or above induces grain growth(recrystallization) at a faster rate when Mn is added to a Cu seedlayer. The added Mn also triggers the growth of Cu grains down to thebottom surface of the metal line so that a true bamboo microstructurereaching to the bottom surface is formed and the Cu diffusion mechanismalong grain boundaries oriented along the length of the metal line iseliminated.

Manganese (Mn) is added to the copper (Cu) seed layer, the copper (Cu)plating layer or the copper (Cu) capping layer in order to modify themicrostructure of copper (Cu) lines and vias. The manganese (Mn) can bein the form of a copper manganese alloy or as a very thin manganese (Mn)layer. The manganese (Mn) can promote normal grain growth (growth of allorientations simultaneously) or abnormal grain growth (growth of certainorientations preferential to others) in the fine lines and vias leadingto bamboo grains (spanning the line width and height). Tailored to occurat a distance less than the “Blech” length, the grain boundariesconfigured in bamboo microstructure in the inventive metal interconnectstructure shut down copper (Cu) grain boundary diffusion. At least onebamboo grain (at right angles to the current flow) every “Blech” lengthacts as a blocking site for copper (Cu) diffusion. The composition ofthe metal interconnect structure after grain growth contains from about1 ppm to about 10% of manganese (Mn) in atomic concentration.

Referring to FIG. 1, a metal interconnect structure according to a firstembodiment of the present invention includes a dielectric layer 110, ametallic barrier layer 120, a copper-manganese alloy seed layer 130, anda plated copper-containing layer 140. The dielectric layer 110 istypically formed on a semiconductor substrate (not shown) containingsemiconductor devices (not shown). The dielectric layer 110 includes adielectric material such as silicon oxide (SiO), silicon nitride (SiN),organosilicate glass (OSG), SiCOH, a spin-on low-k dielectric materialsuch as SiLK™, etc. The dielectric layer 110 may be porous ornon-porous. A via cavity overlaps with the line cavity in an integrationscheme that is known in the art as dual damascene integration scheme.

For illustrative purposes, the present invention is described for a dualdamascene integration scheme. However, variations of the presentinvention in a single damascene integration scheme are contemplated, inwhich the metal vias and metal lines are formed by two separatedelectroplating processes. In the event a single damascene integrationscheme is used, the methods of the present invention are preferablyrepeated twice, a first time, to form the metal vias containing acopper-manganese alloy and having a single grain or large grains withboundaries running perpendicular to the via (parallel to the substrate),and a second time, to form metal lines containing a copper-manganesealloy having the same bamboo structure as the bamboo structure to bedescribed below for the dual damascene integration scheme.

The metallic barrier layer 120 is formed to prevent diffusion ofcontaminants from and/or into a metal via and a metal line to besubsequently formed, as well as to promote adhesion of the metal via andthe metal line to the dielectric layer 110. The metallic barrier layer120 may include Ta, TaN, W, WN, TiN, or a stack thereof such as Ta/TaN,Ta/TaN/Ta, TaN/Ta, etc. The metallic barrier layer 120 may be formed bychemical vapor deposition (CVD), physical vapor deposition (PVD), atomiclayer deposition (ALD), etc. The thickness of metallic barrier layer120, as measured at a bottom surface of the line cavity, ranges fromabout 1 nm to about 25 nm, and typically from about 3 nm to about 10 nm,although lesser and greater thicknesses are also contemplated herein.

The copper-manganese alloy seed layer 130 is formed on the metallicbarrier layer 120, for example by physical vapor deposition (PVD),chemical vapor deposition, atomic layer deposition (ALD),electrodeposition, or electroless deposition. The copper-manganese alloyseed layer 130 is a copper-containing seed layer, which also includesmanganese, i.e., includes an alloy of copper and manganese. Theconcentration of manganese in the copper-manganese alloy seed layer 130may be from about 1 ppm to 10 atomic percent and preferably from about10 ppm to about 2 atomic percent. Incorporation of manganese into thecopper-manganese alloy 130 may be effected, for example, by replacingpure copper in a sputtering target of a PVD process with a targetcontaining a copper-manganese alloy.

The copper-manganese alloy seed layer 130, as deposited, has apolycrystalline structure in which the average size of the grains iscomparable with the thickness of the copper-manganese alloy seed layer130 or less. Typically, the copper-manganese alloy seed layer 130 has anaverage grain size from about 2 nm to about 10 nm. The thickness of thecopper-manganese alloy seed layer 130, as measured above a bottomsurface of the line cavity, may be from about 2 nm to about 60 nm andtypically from about 5 nm to about 50 nm, although lesser and greaterthicknesses are also contemplated herein.

The plated copper-containing layer 140 is formed by plating acopper-containing material on the copper-manganese alloy seed layer 130.The plating process may employ electroplating or electroless plating.The plated copper-containing layer 140, due to the nature of the processemployed for formation, i.e., due to the nature of the plating process,includes O, N, C, Cl, and S. The sum of concentrations of O, N, C, Cl,and S is typically from about 1 ppm to about 200 ppm. Preferably, theplated copper-containing layer 140 is formed by electroplating.Typically, a superfill (bottom-up fill) process is employed to preventformation of any seam within the via cavity or the line cavity so thatthe plated copper-containing layer 140 is free of any cavity therein.

The plated copper-containing layer 140 may, or may not, includemanganese. In one case, the plated copper-containing layer 140 mayconsist essentially of copper, so that any material other than copper inthe plated copper-containing layer 140 is at a trace level. In anothercase, the plated copper-containing layer 140 may include acopper-manganese alloy with a manganese concentration from about 1 ppmto 10 atomic percent, and preferably from about 10 ppm to about 2 atomicpercent. Incorporation of manganese into the plated copper-containinglayer 140 may be effected by replacing a plating bath containing asolution of a copper-manganese alloy, i.e., adding manganese to theplating bath so that manganese is incorporated into the film duringplating.

The thickness of the plated copper-containing layer 140, as measuredoutside the area containing the via cavity and the line cavity prior tothe filling thereof by the plated copper-containing layer 140, may befrom about 40 nm to about 800 nm, and typically from about 100 nm toabout 300 nm, although lesser and greater thicknesses are contemplatedherein also. As deposited, the plated copper-containing layer 140 has amicrostructure in which the grain size is from about 5 nm to about 400nm, and typically from about 10 nm to about 200 nm, although the grainsize depends on the details of the plating process and may be less thanor greater than the range indicated above.

The first exemplary metal interconnect structure is subjected to arecrystallization process in which the grains in the copper-manganesealloy seed layer 130 and the plated copper-containing layer 140 grow.The recrystallization process typically employs an anneal at atemperature from about 20° C. to about 400° C. for a time period fromabout 1 second to about 1 week. The grain size increases during theannealing within the copper-manganese alloy seed layer 130 and theplated copper-containing layer 140. While an anneal above 50° C. ispreferred, some degree of recrystallization occurs at room temperatureso that the present invention may be advantageously employed evenwithout an anneal process, i.e., by leaving the first exemplary metalinterconnect structure alone at room temperature from an extended time,and thereby increasing the size of the grains.

The manganese added into copper-manganese alloy seed layer 130 affectsthe microstructure of a copper-manganese alloy layer, which is formed bythe recrystallization of the copper-manganese alloy seed layer 130 andthe plated copper-containing layer 140, after the recrystallizationprocess. Manganese forms no intermetallic compounds with copper. Thus,manganese precipitates in the grain boundaries during therecrystallization process. Manganese also induces growth of large grainseven at the interface with the metallic barrier layer 120 such that thesize of the grains is substantially the same at the top of thecopper-manganese alloy layer as at the bottom of the copper-manganesealloy layer.

According to the present invention, manganese in the copper-manganesealloy seed layer 130 nucleates new grains in the platedcopper-containing layer 140 so that the grains in the platedcopper-containing layer 140 may grow to dimensions larger than thefeature size of metal lines to be subsequently formed. Further, graingrowth extends into the copper-manganese alloy seed layer 130 so thatthe entirety of the copper-manganese alloy layer is affected by thegrain growth. In addition, the plated copper-containing layer 140 mayoptionally supply additional manganese to accelerate the grain growthduring the recrystallization process.

The copper-manganese alloy layer, which has been through therecrystallization process, has grain sizes larger than the thickness asmeasured over a line feature area of the copper-manganese alloy layer tothe top surface of the dielectric layer 110. The bottom portion of thecopper-manganese alloy layer, including the portions corresponding tothe via cavity and the line cavity prior to formation of thecopper-manganese alloy seed layer 130, in the first exemplary metalinterconnect structure contains substantially few small grains. Thegrain size of the bottom portion of the copper-manganese alloy layer issubstantially the same as the grain size of the top portion of thecopper-manganese alloy layer, and is thus greater than the thickness ofthe copper-manganese alloy layer. The absence of a network of small sizegrains at the bottom portion of the copper-manganese alloy layerprevents diffusion of copper atoms or manganese atoms along a grainboundary. Grain boundaries that are present within a recessed linefeature tend to run in the direction of the width of the recessed linefeature. Thus, the grain boundaries in the copper-manganese alloy layersubstantially do not join one another, and the copper-manganese alloylayer has a bamboo microstructure in which grain boundaries within thebamboo microstructure extend to a bottom surface of copper-manganesealloy layer and separated from one another by at least one grain. Abamboo grain every “Blech” length substantially stops electromigrationinduced by grain boundary diffusion.

The copper-manganese alloy layer is planarized, for example, by chemicalmechanical planarization, to form a copper-manganese alloy line that issubstantially coplanar with a top surface of the dielectric layer 110.The grain size near the top surface of the copper-manganese alloy linemay be about, or greater than, 2 to 3 times the width of thecopper-manganese alloy line. Thus, the copper-manganese alloy linesubstantially has a bamboo microstructure throughout and is free ofsmall grains having a size less than the width of the copper-manganesealloy line. The bamboo-style segmentation between grain boundaries issubstantially present throughout the entirety of the copper-manganesealloy line. The bamboo microstructure eliminates copper diffusion alonggrain boundaries since any remaining grain boundaries are substantiallyperpendicular to the direction of current flow.

Referring to FIG. 2, a second exemplary metal interconnect structureaccording to a second embodiment of the present invention includes adielectric layer 110, a metallic barrier layer 120, a copper-containingseed layer 230, and a plated copper-manganese alloy layer 240. Thedielectric layer 110 is typically formed on a semiconductor substrate(not shown) containing semiconductor devices (not shown) and may includethe same materials as in the first embodiment. A via cavity and a linecavity are formed within the dielectric layer 110 by lithographicpatterning and etching such that the via cavity overlaps with the linecavity in an integration scheme that is known in the art as a dualdamascene integration scheme. The metallic barrier layer 120 is formedin the same manner as, and has the same composition and thickness as inthe first embodiment.

The copper-containing seed layer 230 is formed on the metallic barrierlayer 120, for example, by physical vapor deposition (PVD), chemicalvapor deposition (CVD), atomic layer deposition (ALD), electrodepositionor electroless deposition. The copper-containing seed layer 230 may, ormay not, include manganese. In one case, the copper-containing seedlayer 230 may consist essentially of copper, so that any material otherthan copper in the copper-containing seed layer 230 is at a trace level.In another case, the copper-containing seed layer 230 may include acopper-manganese alloy with a manganese concentration from about 1 ppmto 10 atomic percent and preferably from about 10 ppm to about 2 atomicpercent. Incorporation of manganese into the copper-containing seedlayer 230 may be effected, for example, by replacing pure copper in asputtering target of a PVD process with a target containingcopper-manganese alloy.

The copper-containing seed layer 230, as deposited, has apolycrystalline structure in which the average size of the grains iscomparable with the thickness of the copper-containing seed layer 230 orless. Typically, the copper-containing seed layer 230 has an averagegrain size from about 2 nm to about 10 nm. The thickness of thecopper-containing seed layer 230, as measured above a bottom surface ofthe line cavity, may be from about 2 nm to about 60 nm, and typicallyfrom about 5 nm to about 50 nm, although lesser and greater thicknessesare also contemplated herein.

The plated copper-manganese alloy layer 240 is formed by plating acopper-manganese alloy on the copper-containing seed layer 230. Theplating process may employ electroplating or electroless plating. Theplated copper-manganese alloy layer 240, due to the nature of theprocess employed for formation, i.e., due to the nature of the platingprocess, includes O, N, C, Cl and S. The sum of concentrations of O, N,C, Cl and S is typically from about 1 ppm to about 200 ppm. Preferably,the plated copper-manganese alloy layer 240 is formed by electroplating.Typically, a superfill (bottom-up fill) process is employed to preventformation of any seam within the via cavity or the line cavity so thatthe plated copper-manganese alloy layer 240 is free of any cavitytherein.

The plated copper-manganese alloy layer 240 is a copper containing layerwhich also includes manganese, that is, includes an alloy of copper andmanganese. Not necessarily but preferably, metallic components of theplated copper-manganese alloy layer 240 may consist of copper andmanganese. The concentration of manganese in the plated copper-manganesealloy layer 240 may be from about 1 ppm to about 10 atomic percent, andpreferably from about 10 ppm to about 2 atomic percent. Incorporation ofmanganese into the plated copper-manganese alloy layer 240 may beeffected, for example, by replacing a plating bath containing a solutionof pure copper with plating bath containing a solution ofcopper-manganese alloy, that is, adding manganese to the plating bath sothat manganese is incorporated into the film during plating.

The thickness of the plated copper-manganese alloy layer 240, asmeasured outside the area containing the via cavity and the line cavityprior to the filling thereof by the plated copper-containing layer, maybe from about 40 nm to about 800 nm, and typically from about 100 nm toabout 300 nm, although lesser and greater thicknesses are contemplatedherein also. As deposited, the plated copper-manganese alloy layer 240has a microstructure in which the grain size is from about 5 nm to about400 nm, and typically from about 10 nm to about 200 nm, although thegrain size depends on the details of the plating process and may be lessthan or greater than the range indicated above.

The second exemplary metal interconnect structure is subjected to arecrystallization process in which the grains in the copper-containingseed layer 230 and the plated copper-manganese alloy layer 240 grow.After the recrystallization process, the second exemplary metalinterconnect structure is substantially the same as the first exemplarymetal interconnect structure of FIG. 1 of the first embodiment. Thecopper-containing seed layer 230 and the plated copper-manganese alloylayer 240 constitute a copper-manganese alloy layer. The same kind ofrecrystallization process may be employed as in the first embodiment,and the grain size increases in the same manner as in the firstembodiment. The manganese added into plated copper-manganese alloy layer240 affects the microstructure of a copper-manganese alloy layer, whichis formed by the recrystallization of the copper-containing seed layer230 and the plated copper-manganese alloy layer 240. Manganeseprecipitates in the grain boundaries during the recrystallizationprocess in the same manner as in the first embodiment. Manganese inducesgrowth of large grains even at the interface with the metallic barrierlayer 220 such that the size of the grains is substantially the same atthe top of a copper-manganese alloy layer, which is substantially thesame as the copper-manganese alloy layer, 140 in FIG. 1, as the bottomof the copper-manganese alloy layer.

The second exemplary metal interconnect structure is substantially thesame as the first exemplary metal interconnect structure as shown inFIG. 1. The copper-manganese alloy layer is planarized in the samemanner as in the first embodiment to form a copper-manganese alloy line.The second exemplary metal interconnect structure at this point issubstantially the same as the first exemplary metal interconnectstructure in FIG. 1. The second exemplary metal interconnect structureincludes the copper-manganese alloy line, which substantially has abamboo microstructure, and is free of a network of small grains having asize less than the width of the copper-manganese alloy line. Thebamboo-style segmentation between grain boundaries is substantiallypresent through the copper-manganese alloy line as in the firstexemplary metal interconnect structure. Thus, the bamboo microstructureeliminates copper diffusion along grain boundaries because any remaininggrain boundaries are substantially perpendicular to the direction ofcurrent flow.

Referring to FIG. 3, a third exemplary metal interconnect structureaccording to a third embodiment of the present invention includes adielectric layer 110, a metallic barrier layer 120, a copper-containingseed layer 330, plated copper-containing layer 340, and acopper-manganese alloy cap layer 350. The dielectric layer 110 istypically formed on a semiconductor substrate (not shown) containingsemiconductor devices (not shown), and may include the same material asin the first embodiment. A via cavity and a line cavity is formed withinthe dielectric layer 110 by lithographic patterning and etching suchthat the via cavity overlaps with the line cavity in an integrationscheme that is known in the art as a dual damascene integration scheme.The metallic barrier layer 120 is formed in the same manner as, and hasthe same composition and thickness as, in the first embodiment.

The copper-containing seed layer 330 is formed on the metallic barrierlayer 120, for example, by physical vapor deposition (PVD), chemicalvapor deposition (CVD), atomic layer deposition (ALD),electrodeposition, or electroless deposition. The copper-containing seedlayer 330 may, or may not, include manganese. In one case, thecopper-containing seed layer 330 may consist essentially of copper, sothat any material other than copper in the copper-containing seed layer330 is at a trace level. In another case, the copper-containing seedlayer 330 may include a copper-manganese alloy with a manganeseconcentration from about 1 ppm to 10 atomic percent, and preferably fromabout 10 ppm to about 2 atomic percent. Incorporation of manganese intothe copper-containing seed layer 330 may be effected, for example, byreplacing pure copper in a sputtering target of a PVD process with atarget containing a copper-manganese alloy. The copper-containing seedlayer 330, as deposited, may have the same polycrystalline structure andthickness as in the first embodiment.

The plated copper-containing layer 340 is formed by plating acopper-containing material on the copper-containing seed layer 330. Theplating process may employ electroplating or electroless plating. Theplated copper-containing layer 340, due to the nature of the processemployed for formation, that is, due to the nature of the platingprocess, includes O, N, C, Cl and S. The sum of concentrations of O, N,C, Cl and S is typically from about 1 ppm to about 200 ppm. Preferably,the plated copper-containing layer 340 is formed by electroplating.Typically, a superfill (bottom-up fill) process is employed to preventformation of any seam within the via cavity or the line cavity so thatthe plated copper-containing layer 340 is free of any cavity therein.

The plated copper-containing layer 340 may, or may not, includemanganese. In one case, the plated copper-containing layer 340 mayconsist essentially of copper, so that any material other than copper inthe plated copper-containing layer 340 is at a trace level. In anothercase, the plated copper-containing layer 340 may include acopper-manganese alloy with a manganese concentration from about 1 ppmto 10 atomic percent, and preferably from about 10 ppm to about 2 atomicpercent. Incorporation of manganese into the plated copper-containinglayer 340 may be effected by replacing a plating bath containing asolution of pure copper with a plating bath containing a solution ofcopper-manganese alloy, that is, adding manganese to the plating bath sothat manganese is incorporated into the film during plating. Themicrostructure and the thickness of the plated copper-containing layer340 may be the same as in the first embodiment.

The copper-manganese alloy cap layer 350 includes an alloy of copper andmanganese, and may consist of an alloy of copper and manganese. Theconcentration of manganese in the copper-manganese alloy cap layer 350may be from about 1 ppm to about 50 atomic percent, and preferably fromabout 10 ppm to about 40 atomic percent, and more preferably from about100 ppm to about 30 atomic percent. The copper-manganese alloy cap layer350 may be formed, for example, by physical vapor deposition (PVD),chemical vapor deposition (CVD), atomic layer deposition (ALD),electrodeposition, or electroless deposition.

The thickness of the copper-manganese alloy cap layer 350 may be fromabout 1 nm to about 50 nm, and typically from about 3 nm to about 30 nm,although lesser and greater thicknesses are contemplated herein also. Asdeposited, the copper-manganese alloy cap layer 350 has a microstructurein which the grain size is from about 2 nm to about 20 nm, and typicallyfrom about 5 nm to about 10 nm, although grain size depends on thedetails of the deposition process and may be less than or greater thanthe range indicated above.

The third exemplary metal interconnect structure is subjected to arecrystallization process in which the grains grow in thecopper-manganese alloy cap layer 350, the plated copper-containing layer340, and the copper-containing seed layer 330. After therecrystallization process, the third exemplary metal interconnectstructure is substantially the same as the first exemplary metalinterconnect structure of FIG. 1 of the first embodiment. Thecopper-manganese alloy cap layer 350, the plated copper-containing layer340, and the copper-containing seed layer 330 collectively become acopper-manganese alloy layer. The same kind of recrystallization processmay be employed as in the first embodiment, and the grain size increasesin the same manner as in the first embodiment. The manganese added intothe copper-manganese alloy cap layer 350 affects the microstructure of acopper-manganese alloy layer after the recrystallization process.Manganese precipitates in the grain boundaries during therecrystallization process in the same manner as in the first embodiment.Manganese induces growth of large grains at the top interface with thecopper-manganese cap layer 350 such that the size of the grains issubstantially the same at the top of the copper-manganese cap alloylayer as at the bottom of the copper-manganese alloy layer.

Manganese present in the copper-manganese alloy cap layer 350 triggersgrain growth during the recrystallization process. The grain growthextends into the plated copper-containing layer 340 and thecopper-containing seed layer 330 so that the entirety of thecopper-manganese alloy layer, which results from the copper-manganesealloy cap layer 350, the plated copper-containing layer 340, and thecopper-containing seed layer 330, is affected by the grain growth. Ifthe plated copper-containing layer 340 further includes manganese, theadditional manganese in the copper-containing seed layer 330 may alsopromote the grain growth during the recrystallization process.

The third exemplary metal interconnect structure is substantially thesame as the first exemplary metal interconnect structure as shown inFIG. 1, and accordingly, the same physical, compositional, andstructural characteristics. The copper-manganese alloy layer isplanarized in the same manner as in the first embodiment to form acopper-manganese alloy line. The third exemplary metal interconnectstructure at this point is substantially the same as the first exemplarymetal interconnect structure in FIG. 1. The third exemplary metalinterconnect structure includes the copper-manganese alloy line, whichhas a substantially bamboo microstructure, and is substantially free ofsmall grains having a size less than the width of the copper-manganesealloy line. The bamboo-style segmentation between grain boundaries issubstantially present through the copper-manganese alloy line as in thefirst exemplary metal interconnect structure. Thus, the bamboomicrostructure eliminates copper diffusion along grain boundariesbecause any remaining grain boundaries are substantially perpendicularto the direction of current flow. A bamboo grain every “Blech” lengthsubstantially stops electromigration induced by grain boundarydiffusion.

Referring to FIGS. 4A-4E, a method of forming the metal interconnectstructures described above is shown. A dielectric material 110 isprovided on a pre-existing semiconductor structure (not shown). Thedielectric material 110 has been etched to form a recessed line patternin the dielectric material 110. A metallic barrier layer 120 is formedon the dielectric material 110. Preferably, the metallic barrier layer120 is formed along a top portion and sidewalls of the recessed linepattern in dielectric material 110. A copper-containing seed layer 430is formed on the metallic barrier layer, preferably on a top portion andon sidewalls of the recessed line pattern on the dielectric material110. A copper-containing layer 440 is deposited and electroplated on thecopper-containing seed layer 430. At least one of the copper-containingseed layer 430 and copper-containing layer 440 includes acopper-manganese alloy. The copper-manganese alloy contains a manganeseconcentration from about 1 ppm to about 10 atomic percent. Preferably,the copper-manganese alloy contains a manganese concentration from about10 ppm to about 2 atomic percent. A copper-manganese alloy cap layer 350may also be formed on the copper-containing layer 440. Thecopper-manganese alloy cap layer 350 preferably has a manganeseconcentration from about 1 ppm to about 50 atomic percent.

The copper-containing seed layer 430 and the copper-containing layer 440are annealed at a temperature from about 20° C. to about 400° C. for atime period from about 1 second to about 1 week. During the annealingprocess, the grain size increases in the copper-containing layer 440 andthe copper-containing seed layer 430. The increase in grain size alsodecreases resistance within the copper-containing seed layer 430 and thecopper-containing layer 440. The copper-containing seed layer 430 andcopper-containing layer 440 substantially form a bamboo microstructurewithin the recessed line pattern. Grain boundaries within the bamboomicrostructure extend to a bottom surface of the copper-containing layer440 at least every “Blech” length. Some of the manganese (Mn) willdiffuse to the surfaces of the recessed line pattern and react with anyavailable oxygen (O₂) forming a manganese oxide (MnO) or manganesesilicate (MnSiO) layer, thus removing the manganese alloy from thecopper (Cu). The grain size may be increased in such a way that grainboundaries are separated from one another by at least a width of a metalline at a bottom surface of the metal line.

As shown in FIG. 5, the copper-containing layer 440 is planarized,stopping at the top of the dielectric layer. A remaining portion of thecopper-containing seed layer 430 and the copper-containing layer 440constitutes a copper-manganese alloy line. The grain size measured at abottom of the copper-manganese alloy line can exceed a width of thecopper-manganese alloy line. The copper-manganese alloy linesubstantially has a bamboo microstructure where each grain boundaryextends from a top surface of the copper-manganese alloy line to abottom surface of the copper-manganese alloy line and is separated fromany other grain boundary by a distance greater than the width of thecopper-manganese alloy line.

FIG. 6 shows a plot of percentage decrease in sheet resistance versustime at room temperature for a 500 nm plated copper film on a 30 nmCu—Mn seed layer on a silicon oxide. The percentage of Mn in the copperseed layer ranges from 0.15 to 0.84 atomic percent Mn. It is clear thatthe plated Cu sheet resistance drops much quicker on the Cu—Mn seedlayers with 0.84 atomic percent Mn showing fastest drop, complete within5 hrs. The sheet resistance is a measure of the room temperature Cugrain growth (recrystallization), which is well known for plated Cufilms. The Mn enhances the recrystallization. After 11.5 days, the pureCu seed layer shows a sheet resistance drop of only approximately 8%,whereas on the Cu—Mn seed layers recrystallization is complete afterapproximately 1.5 days.

FIG. 7 similarly illustrates a percentage decrease in sheet resistanceversus time at room temperature for a plated copper film on a Cu—Mn seedlayer on a silicon oxide. In FIG. 7, the thickness of the plated Cu filmis 300 nm thick. Again, the Cu—Mn seed layers enhance the Curecrystallization, with the 0.84 atomic percent Mn showing the fastestrecrystallization rate.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A metal interconnect structure, comprising: a dielectric materiallayer containing a recessed line pattern; a metallic barrier layerabutting the dielectric material layer at sidewalls of the recessed linepattern and overlying an entirety of the dielectric material layer; acopper-containing seed layer abutting the metallic barrier layer andoverlying an entirety of the dielectric material layer; and acopper-containing layer comprising electroplated copper and abutting thecopper-containing seed layer, wherein at least one of thecopper-containing seed layer and the copper-containing layer comprises acopper-manganese alloy, and wherein the copper-containing seed layer andthe copper-containing layer form a bamboo grain within the recessed linepattern, the grain size measured at a bottom surface of thecopper-containing layer exceeding a width of the copper-manganese alloyline at least every “Blech” length.
 2. The structure of claim 1, whereinthe copper-containing layer comprises O, N, C, Cl and S, a sum ofconcentrations of which ranges from about 1 ppm to about 200 ppm.
 3. Thestructure of claim 1, wherein at least one of the copper-containing seedlayer and the copper-containing layer contains a manganese concentrationfrom about 1 ppm to about 10 atomic percent.
 4. The structure of claim1, wherein the copper-manganese alloy contains a manganese concentrationfrom about 10 ppm to about 2 atomic percent.
 5. The structure of claim1, wherein the copper-containing seed layer comprises a copper-manganesealloy containing a manganese concentration from about 1 ppm to about 10atomic percent and has a thickness from about 2 nm to about 60 nm. 6.The structure of claim 1, wherein the copper-containing layer comprisesa copper-manganese alloy containing a manganese concentration from about1 ppm to about 10 atomic percent and has a thickness from about 40 nm toabout 800 nm above a portion of the dielectric material layer locatedoutside the recessed line pattern.
 7. A metal interconnect structure,comprising: a dielectric material layer containing a recessed linepattern; a metallic barrier layer abutting the dielectric material layerat sidewalls of the recessed line pattern and overlying an entirety ofthe dielectric material layer; a copper-containing seed layer abuttingthe metallic barrier layer and overlying an entirety of the dielectricmaterial layer; a copper-containing layer comprising electroplatedcopper and abutting the copper-containing seed layer, wherein thecopper-containing seed layer and the copper-containing layer form abamboo grain within the recessed line pattern, the grain size measuredat a bottom surface of the copper-containing layer exceeding a width ofthe copper-manganese alloy line at least every “Blech” length; and acopper-manganese alloy cap layer abutting the copper-containing layer.8. The structure of claim 7, wherein the copper-containing layercomprises O, N, C, Cl, and S, a sum of concentrations of which is fromabout 1 ppm to about 200 ppm.
 9. The structure of claim 8, wherein thecopper-manganese alloy contains a manganese concentration from about 10ppm to about 20 atomic percent.
 10. The structure of claim 7, whereinthe copper-manganese alloy cap layer contains a manganese concentrationfrom about 1 ppm to about 50 atomic percent.
 11. A metal interconnectstructure, comprising: a plated copper layer containing a line pattern;a copper-manganese seed layer having an atomic concentration ofmanganese from about 1 ppm to about 20 atomic percent at the bottomsurface of the plated copper line sandwiched between the plated copperline and a barrier layer all of which are patterned, wherein a grainsize measured at a bottom of the copper-manganese alloy line exceeds awidth of the copper-manganese alloy line at least every “Blech” length;and a barrier and dielectric layer surrounding the copper manganesealloy line.
 12. A method of forming a metal interconnect structure,comprising: providing a dielectric material layer containing a recessedline pattern; forming a metallic barrier layer on the dielectricmaterial layer at sidewalls of the recessed line pattern; forming acopper-containing seed layer on the metallic barrier layer; andelectroplating a copper-containing layer on the copper-containing seedlayer, wherein at least one of the copper-containing seed layer and thecopper-containing layer comprises a copper-manganese alloy containing amanganese concentration from about 1 ppm to about 10 atomic percent. 13.The method of claim 12, further comprising: annealing thecopper-containing seed layer and the copper-containing layer at atemperature from about 20° C. to about 400° C. for a time period fromabout 1 second to about 1 week, wherein grain size increases during theannealing within the copper-containing layer and the copper-containingseed layer.
 14. The method of claim 13, further comprising: increasinggrain size and decreasing resistance within the copper-containing seedlayer and the copper-containing layer, wherein the copper-containingseed layer and the copper-containing layer form a bamboo grain withinthe recessed line pattern, and wherein each bamboo grain boundary withinthe bamboo microstructure extends to a bottom surface of thecopper-containing layer and repeats at least every “Blech” length. 15.The method of claim 14 wherein the grain size may be increased withinthe copper-containing seed layer and the copper-containing layer suchthat grain boundaries are separated from one another by at least a widthof a metal line at a bottom surface of the metal line.
 16. The method ofclaim 12, further comprising: planarizing the copper-containing layer,wherein a remaining portion of the copper-containing seed layer and thecopper-containing layer constitutes a copper-manganese alloy line,wherein a grain size measured at a bottom of the copper-manganese alloyline exceeds a width of the copper-manganese alloy line at least every“Blech” length.
 17. The method of claim 12, wherein the copper-manganesealloy line has a bamboo microstructure where each grain boundary extendsfrom a top surface of the copper-manganese alloy line to a bottomsurface of the copper-manganese alloy line, and is separated from anyother grain boundary by a distance greater than the width of thecopper-manganese alloy line.
 18. The method of claim 12, wherein thecopper-containing seed layer comprises a copper-manganese alloycontaining a manganese concentration from about 1 ppm to about 10 atomicpercent, and wherein the copper-containing seed layer is formed byphysical vapor deposition (PVD), chemical vapor deposition (CVD), atomiclayer deposition (ALD), electrodeposition, or electroless deposition.19. A method of forming a metal interconnect structure, comprising:providing a dielectric material layer containing a recessed linepattern; forming a metallic barrier layer directly on the dielectricmaterial layer at sidewalls of the recessed line pattern; forming acopper-containing seed layer directly on the metallic barrier layer;electroplating a copper-containing layer directly on thecopper-containing seed layer; and forming a copper-manganese alloy caplayer containing a manganese concentration from about 1 ppm to about 50atomic percent directly on the copper-containing layer.
 20. The methodof claim 19, further comprising: increasing grain size and decreasingresistance within the copper-containing seed layer and thecopper-containing layer, wherein the copper-containing seed layer andthe copper-containing layer form bamboo grains within the recessed linepattern, and wherein each bamboo grain boundary within the bamboomicrostructure extends to a bottom surface of the copper-containinglayer and repeats at least every “Blech” length.
 21. The method of claim19, further comprising: planarizing the copper-containing layer, whereina remaining portion of the copper-containing seed layer and thecopper-containing layer constitutes a copper-manganese alloy line,wherein a grain size measured at a bottom of the copper-manganese alloyline exceeds a width of the copper-manganese alloy line and repeats atleast every “Blech” length.
 22. The method of claim 19, wherein thecopper-manganese alloy line has a bamboo microstructure, wherein eachgrain boundary extends from the top surface of the copper-manganesealloy line to a bottom surface of the copper-manganese alloy line, andis separated from any other grain boundary by a distance greater thanthe width of the copper-manganese alloy line.